DON: Don't wipe it away, Nat. Let me have my little vicious circle. You know, the circle is the perfect geometric figure. No end; no beginning.
Circles pop up frequently in The Lost Weekend, which we see as a neat little metaphor for the cycle of addiction. Don's boozy benders could certainly be described as "little vicious circles" and, what's more, they frequently feel like they have no end and no beginning.
DON: I may never touch it while I'm there, not a drop. What you don't understand is that I've got to know it's around. That I can have it if I need it.
If Don doesn't have a bottle of booze around, he feels such intense anxiety that he can hardly think straight (though to be fair, he can hardly think straight when the booze is around, either). This is a very common mindset for an addict, however.
DON: It shrinks my liver. It pickles my kidneys, yes. But what does it do to my mind? It tosses the sandbags overboard so the balloon can soar.
Although Don's alcoholism is clearly ruining his life, we can't deny that the dude becomes more eloquent after a few shots. He even quotes Shakespeare. If he has one too many, however, that witty charmer quickly transforms into a regular old sloppy drunk.
HELEN: He's a sick person. It's as though something were wrong with his heart or lungs. You wouldn't walk out on him if he had an attack.
These days, it's pretty common to think of alcoholism and other addictions as medical conditions rather than moral ones, but that perspective was a lot less accepted back in the 1940's when the film was made. Major props to Helen for this one.
DON: That's when you need it most—in the morning. Haven't you learned that yet? At night, the stuff's a drink. In the morning, it's medicine.
There's a definite contrast between Morning Don and Night Don. When Night Don drinks, he's having a good time. When Morning Don drinks, however, he's simply trying to survive. With this, the negative consequences of Don's alcoholism are finally coming into focus.
[While performers dance in an opera, they transform in Don's mind to dancing trench coats with bottles of whiskey in their front pockets.]
This scene doesn't say anything about Don's condition that we don't already know, but it's such a crazy moment that we <em>had to</em> include it. Though it borders on <em>Looney Tunes</em> -levels of silliness, it also shows how far Don has detached from reality.
HELEN: What guy? Who are you talking about?
DON: The other Don Birnam. There are two of us, you know—Don the Drunk and Don the Writer.
During the flashback in which Helen discovers Don's alcoholism, we see Don make a distinction between his drunk self and his true, writer self. That's an interesting idea. What's more, it shows us that Don sees his alcoholism as something that is separate from himself in many ways.
NAT: That's all.
DON: Come on, Nat. I'll let you have my typewriter.
Here, Don is getting perilously close to rock bottom. His willingness to sell his typewriter—the symbol of his dream to become a writer—reveals that Don the Drunk now reigns victorious.
BIM: You're an alkie, you'll come back. They all do.
Although Bim's dedicated his life to helping alcoholics, he's not a very sympathetic guy. It's odd. Most notably, he mocks Don for having the gall to think that he could ever be cured.
HELEN: Of course you couldn't write the beginning because you didn't know the ending. Only now–
[Don picks up a glass of whiskey and contemplates it before dropping his cigarette in it]
HELEN: Only now you know the ending.
Of course, Bim turns out to be as wrong as wrong could be—Don does indeed walk away from The Lost Weekend a cured man. For now, at least. No matter how things end up, however, we see here that Don is making an active choice to refuse alcohol, and that's a good start. As a side note, this is a subtle nod to the first drink Don takes in the film, which he contemplates throwing a match into—remember those circles?